This application is a xc2xa7371 U.S. National Phase application which bases priority on International Application No. PCT/DE 99/02307, filed Jul. 22, 1999, which in turn bases priority on German Application No. DE 198 34 781.2, filed Aug. 1, 1998.
1. Field of the Invention
The invention relates to a method for determining varying ice concentrations in binary ice volumes. Binary ice, i.e. a suspension of small ice crystals in an aqueous solution or mixture, is used in widely varying forms for refrigerated transportation, refrigerated storage and refrigerated use.
2. Description of the Prior Art
Unlike in the case of other, single-phase liquid coolants (e.g. water, brine, etc.) there is no or only an insignificant binary ice temperature change for as long as ice crystals are present in this two-phase fluid. Heat supply does not lead to a significant temperature rise and instead the ice crystals melt (latent energy).
To be able to control the use of binary ice, it is necessary to determine the ice concentration in the binary ice volume. This has hitherto been carried out inter alia by the measurement of the electrical conductivity or electrical conduction resistance, as well as the measurement of the pressure in a closed storage container and in each case only an indirect conclusion concerning the ice concentration is possible, which is in particular inadequate if the external framework conditions do not remain constant.
Thus, e.g. in systems where the chemical composition of the binary ice fluid is not constant, the electrical conductivity cannot be a reliable measure for the ice concentration. The same applies for non-closed systems with a non-constant mass, in which volume changes would be expressed as an ice concentration change, which leads to errors. The measurement of the density of the binary ice fluid is very complicated and must be eliminated for cost reasons, particularly in smaller plants. A determination of the viscosity of the binary ice fluid as a measure for the ice concentration is impossible with conventional methods, because binary ice is a non-Newtonian fluid (it is a Bingham fluid) and consequently does not supply a usable signal for the ice concentration.
Calorimetric determinations of the ice concentration are only suitable on a laboratory scale, because they require manual measures.
For a discussion of the state of the art, U.S. Pat. No. 4,888,976 is named, wherein an apparatus for recording the viscosity of a lubricant is described in which components to be provided additionally with at least two parts are proposed, and which are positioned movable in relation to each other and which are driven by a motor. Also WO 97/48973 is known, wherein an impeller rotates in a fluid for measurement of the consistency of a paper pulp or the like. In both references a multitude of additional parts are needed, which makes the measurement technological large scale and the cost of repair expensive.
The problem of the invention is therefore to provide a method with which it is possible to determine the ice concentration in binary ice volumes.
According to the invention this problem is solved by a method having the features of the main claim. The subclaims provide advantageous embodiments of the invention.
Particularly as a result of carrying out mechanical work in the volume to be measured with an electric motor, particularly if the motor drives a scraper configuration, a mathematical conversion is possible, which enables conclusions to be drawn regarding the ice concentration from the electric power determined.
However, it is also conceivable to use a stirrer in an ice accumulator, optionally in addition to the scraper configuration, for a more precise mathematical conversion. It is also possible to use the electric power of a binary ice fluid-delivering pump for determining the ice concentration.
It is additionally possible to measure the pump pressure, which is produced on conveying binary ice in a pipeline. This pressure is not related to the binary ice pressure through expansion with increasing ice concentration.
Further advantages and features of the invention can be gathered from the following description of a preferred embodiment of the method.